The present invention relates to an improved process for production of aromatic polyethers. More particularly, it is concerned with a process for industrially advantageously producing high molecular weight aromatic polyethers excellent in properties such as heat resistance, chemical resistance and mechanical strength by performing polymerization in the presence of compounds having a specified catalytic action for polymerization.
In recent years, aromatic polyethers comprising ether groups and phenylene groups linked together through various functional groups have been attracting attention as materials for molding in various field because they are excellent in properties such as heat resistance, chemical resistance and mechanical strength.
Processes for production of aromatic polyethers can be divided into two groups: the electrophilic aromatic substitution method and the nucleophilic aromatic substitution method.
In accordance with the former method, polymerization is carried out with the liberation of hydrogen halide by the Friedel-Crafts reaction in which a hydrogen linked to an aromatic ring is substituted with a cationic species derived from the corresponding acyl halide by the use of a Lewis acid catalyst such as aluminum chloride, boron trifluoride and hydrogen fluoride. This method, however, has disadvantages from an industrial standpoint because it needs more than a stoichiometric amount of Lewis acid having high corrosiveness.
On the other hand, in accordance with the latter method, polyethers are produced through halogen substitution using a phenoxide anion according to the process as represented by the following formula: EQU MO--Ar--OM+X--Ar'--X.fwdarw.(--O--Ar--O--Ar'--).sub.n +2MX, or MO--Ar'--X.fwdarw.(--O--Ar'--).sub.n +MX
(wherein M is an alkali metal, X is a halogen atom, and Ar and Ar' are each a divalent aromatic radical which contains an electron withdrawing group such as a sulfonyl group or a carbonyl group which activates the halogen atom X).
As the above latter method, for example, a method in which a dialkali metal salt of an aromatic dihydroxy compound containing a carbonyl group and an aromatic dihalide compound (an aromatic dihalide) containing a carbonyl group or a sulfone group are heated at a temperature of 250.degree. to 400.degree. C. in diarylsulfone (see, for example, Japanese Patent Publication No. 22938/1982), and a method in which halophenol and alkali metal carbonate are heated at a temperature of 200.degree. to 400.degree. C. in a solvent (see, for example, Japanese Patent Application Laid-Open No. 5488/1986 and U.S. Pat. No. 4,113,699) are known.
R. N. Johnson et al., Journal of Polymer Science, Part A-1, Vol. 5, pp. 2375-2398 (1967) compared the reactivities of various activated aromatic dihalides with an alkali metal salt of bisphenol A in a dimethylsulfoxide solvent and concluded that aromatic fluorides are much more reactive than aromatic chlorides having the same structure and produce polyethers having a higher degree of polymerization.
Joseph F. Bunnett et al., Chemical Review, Vol. 49, pp. 274-412 (1951), particularly the review at page 333, and Jerry March, Advanced Organic Chemistry, 3rd ed., page 587 describe that the reactivity of halogen atom as a releasing group in the two molecular aromatic nucleophilic substitution reaction is generally in the following order: EQU F&gt;Cl.about.Br.about.I,
which is in agreement with the results of R. N. Johnson et al.
Thus it can be seen from the above publications that in producing polyethers having a high degree of polymerization by the nucleophilic aromatic substitution method, an aromatic fluoro compound is desirable to use as the electrophilic monomer component rather than an aromatic chloride compound.
Particularly in a case where an aromatic halogeno compound does not contain a highly electron withdrawing group in the para- or ortho-position relative to the halogen atom, the halogen atom is activated only insufficiently and, therefore, the aromatic chloro compound is of low reactivity and cannot provide high molecular weight aromatic polyethers although it is of low cost as compared with the corresponding aromatic fluoro compound and thus is much more advantageous over the aromatic fluoro compound from an economic standpoint. Actually this is described also in Japanese Patent Publication No. 10486/1986.
The reactivity of the alkali metal salt of the aromatic hydroxy compound to be used as the nucleophilic monomer component is also significant. Industrially, the sodium or potassium salt is usually used Although the sodium salt is advantageous from an economic standpoint, the potassium salt is often chosen in that nucleophilic properties of phenoxide anion are excellent.
The above-cited publication, Advanced Organic Chemistry, 3rd ed., page 308 describes that the reactivity of an anionic nucleophile varies with alkali metal counter ion, and K.sup.+ &gt;Na.sup.+. Particularly in the condensation polymerization with an aromatic halogen compound in which there is no highly electron withdrawing group in the para- or ortho-position relative to the halogen atom and thus the halogen atom is activated only insufficiently, no high molecular weight polymer can be obtained unless the potassium salt is used.
In order to overcome the above problems, Japanese Patent Application Laid-Open No. 221227/1986 discloses an improved method in which a halophenol or a mixture of an aromatic dihydroxy compound and an aromatic dihalide compound is subjected to condensation polymerization in the presence of a stoichiometric amount of sodium carbonate or sodium hydrogencarbonate and a small amount of the fluoride or chloride of potassium, rubidium or cesium to produce poly (aryletherketone). This method is intended to increase the reactivity of phenoxide anion while using the sodium salt which is of low cost.
The above method, however, does not activate the electrophilic monomer component and, therefore, it is considered that the method is applicable only to aromatic fluoro compounds or aromatic chloro compounds in which the chlorine atom is highly activated by a highly electron withdrawing group existing at the para- or ortho-position relative to the chlorine atom for the aforementioned reasons. In other words, Japanese Patent Application Laid-Open No. 221227/1986 suggests that in the polycondensation between the substantially sodium salt of an aromatic dihydroxy compound as the nucleophilic monomer component and a highly reactive aromatic halide compound as the electrophilic monomer component, addition of the fluoride or chloride of an alkali metal having an atomic number exceeding that of sodium permits production of high molecular weight polymers.
In R. N. Johnson et al., Journal of Polymer Science, Vol. 5, Part A-1, pp. 2415-2427, especially at page 2424, it is described that in the polycondensation reaction of an alkali metal salt of bisphenol A and 4,4'-dichlorodiphenylsulfone in a dimethylsulfoxide solvent, even if anhydrous potassium fluoride is added, no change in viscosity of formed polymer is observed and the reason for this is that the rate of substitution of the chlorine atom with the fluoride ion in the reaction system is slow.
It is also known as described in Japanese Patent Application Laid-Open No. 179228/1986 that in production of aromatic polyethers from an aromatic halide monomer of low reactivity, addition of a copper compound accelerates the polymerization. The addition of a copper compound, however, is accompanied by undesirable phenomena such as incorporation of copper in the formed polymer and coloration, and furthermore, if an easily oxidizable monomer such as hydroquinone is used as the aromatic dihydroxy compound, the copper compound undergoes deterioration, thereby losing the polymerization acceleration effect.